1. Field of Invention
The present invention relates to a substrate processing apparatus and a semiconductor device manufacturing method, and relates in particular to technology for preventing or inhibiting the forming of a natural oxidation film.
The present invention for example is effective for use in heat treatment apparatus (furnaces) for heat treatment of semiconductor wafers (hereinafter called “wafers”) on which semiconductor integrated circuits including semiconductor elements are formed in a method for manufacturing semiconductor integrated circuit devices (hereinafter called “IC”).
2. Description of Related Art
Heat treatment apparatus are widely used in heat treatment processes in IC manufacturing methods for forming a CVD film such as an insulating film, or metallic film or semiconductor film on the wafer and diffusing dopants.
In the prior art, this type of heat treatment apparatus includes a processing chamber for batch processing of multiple wafers held in a boat, a standby chamber for holding the boat in standby before loading and after unloading into/from the processing chamber, a cleaning unit made up of a blower and a filter for supplying a clean atmosphere into the standby chamber, and a boat elevator installed opposite the filter in the standby chamber to raise and lower the boat between the standby chamber and the processing chamber.
A motor serving as the drive device for the boat elevator is usually installed in a motor mount chamber isolated from the standby chamber.
This heat treatment apparatus of the prior art is constructed to blow and circulate nitrogen gas serving as the inert gas from the cleaning unit to the standby chamber and in this way prevents oxygen (O2) in the atmosphere from forming a natural oxidation film on the wafer. This technology is disclosed for example in the patent document 1.
Patent document 1 Japanese Patent Non-Examined Publication No. 2004-119888
In this type of heat treatment apparatus, preventing a natural oxidation film from being formed on the wafer due to oxygen in the atmosphere by blowing and circulating nitrogen gas from the cleaning unit to the standby chamber requires maintaining the oxygen concentration within the standby chamber within a few ppm.
This heat treatment apparatus prevents an inflow of the atmosphere into the standby chamber by maintaining the nitrogen gas within the standby chamber at a positive pressure. In other words, besides setting the case forming the standby chamber to render a high sealing effect, nitrogen gas is supplied into the standby chamber at a higher flow rate than the rate at which nitrogen gas leaks out from gaps in the case.
Therefore, in heat treatment apparatus where a heat treating process is assumed to take place in a nitrogen gas atmosphere, the exhaust duct for exhausting the interior of the standby chamber does not need to be made very large.
In other words, the heat treatment apparatus need only maintain the relation in the following equations.Quantity of atmospheric flow into standby chamber=added supply quantity of nitrogen gas+(circulating atmosphere in standby chamber)Quantity of exhaust atmospheric flow from standby chamber=Quantity of leak or the like from standby chamber+(circulating atmosphere in standby chamber)Quantity of atmospheric flow into standby chamber≧Quantity of exhaust atmospheric flow from standby chamber
On other hand, if there is no need to inhibit formation of a natural oxidation film (for example, when a natural oxidation film does not occur on the type of film in the heat treatment process), then creating a non-circulating air flow (air containing oxygen, hereinafter sometimes called “clean air”) in one direction within the standby chamber is preferable in terms of thermal effects.
This one-way flow can be set by satisfying the following simple equation.Quantity of atmospheric flow into standby chamber=Quantity of exhaust atmospheric flow from standby chamber
In this case, blowing the clean air from one side of the standby chamber towards the other side so that the flow is horizontal to the boat, is preferable in preventing phenomena that particles and organic matter stagnate or accumulate inside the standby chamber.
In other words, the exhaust duct for exhausting the interior of the standby chamber must be a sufficiently large size in order to ensure a clean atmosphere within the standby chamber.
The same heat treatment apparatus must be capable of meeting both of the above needs.
Currently however, exhaust performance is inadequate in cases where the case is highly sealed assuming circulation of the atmosphere within the standby chamber.
Designing the heat treatment apparatus with a large exhaust duct to achieve satisfactory exhaustion leads to the problem of a bad footprint (projected floor area) of the heat treatment apparatus.